Acute heart failure (AHF) is a sudden decline, resulting when the heart cannot pump enough blood to meet the cardiac demands of the body. Signs and symptoms can include dyspnea, edema, and fatigue, which can lead to acute respiratory distress and death. AHF, as well as other cardiovascular diseases, can be caused by deficiency in circulating relaxin.
Relaxin is a 6000 Da heterodimeric polypeptide endocrine and autocrine/paracrine hormone, belonging to the insulin gene superfamily. Relaxin facilitates angiogenesis and contributes to the repair of vascular endothelium. It exerts its effects on the musculoskeletal and other systems through binding its receptor in different tissues, a process mediated by different signaling pathways. There are seven known relaxin family peptides, including relaxin (RLN)1, RLN2, RLN3, and insulin-like peptide (INSL)3, INSL4, INSL5, INSL6. RLN1 and RLN2 are involved in collagen regulation and metabolism in fibroblasts, while RLN3 is specific to the brain. RLN1 and RLN2 are also involved in the hemodynamic changes that occur during pregnancy, including cardiac output, renal blood flow, and arterial compliance. Further, RLN2 mediates vasodilation through increased production of nitric oxide through a phosphorylation cascade. Relaxin is also a cardiac stimulant, and it can cause vasodilation through the inhibition of angiotensin II and endothelin, two potent vasoconstrictors. The hormone has also been shown to increase calcium sensitivity of cardiac myofilaments and increase phosphorylation of the myofilaments by protein kinase C. The force generated by the myofilaments increases while the energy consumption of the cardiac myocytes does not. In the kidneys, relaxin increases creatinine clearance and increases renal blood flow.
Relaxin, a vasoactive peptide, protects the vascular system from overwork, increases renal function, promotes cell growth and survival, and maintains good vessel structure. The administration of relaxin to a subject has therapeutic benefits such as treating and preventing fibrosis e.g., renal fibrosis, cardiac fibrosis or pulmonary fibrosis and cardiovascular disease e.g., acute heart failure, coronary artery disease, microvascular disease, acute coronary syndrome with cardiac dysfunction, or ischemia reperfusion.
The standard of care therapy for many of the disorders associated with relaxin deficiency include beta blockers, hydralazine/isorbide dinitrate, digitalis, diuretics, angiotensin-converting enzyme (ACE) inhibitors, angiotensin-receptor blockers (ARB), digoxin, anticoagulants, aldosterone antagonists, and medications to control co-morbidies, including, but not limited to, high cholesterol, high blood pressure, atrial fibrillation, and diabetes. Lifestyle modifications, including diet and exercise, are also typically recommended.
Although relaxin provides significant therapeutic benefits, recombinant wild type relaxin has a short half-life which makes the achievement of therapeutic levels in the body a challenge. A recombinant form of relaxin referred to as Serelaxin and marketed by Novartis, has been demonstrated to have low toxicity, however, the efficacy has been questionable because it is degraded so quickly in the bloodstream. Serelaxin has a half-life of about 15 minutes in serum and 7-8 hours during continuous 48 hour infusion.